Three dimensional electrode having electron directing members and method of making the same

ABSTRACT

A method of making a three dimensional electrode having an active material layered between a current collector and a separator includes growing nanotubes at predetermined points on a first sheet of electron directing material, wherein the electron directing material is highly conductive and chemically inert; aligning the nanotubes in a direction perpendicular to the first sheet; functionalizing a distal end of each nanotube; bonding a second sheet of electron directing material to the functionalized distal end of each nanotube; depositing magnetic particles along the second sheet; applying a magnetic field to the magnetic particles to rotate the first sheet, the second sheet and the nanotubes ninety degrees to form an electron directing structure; and attaching the electron directing structure on a surface of the current collector with a polymer binder. The electron directing structure is configured to direct electron flow along a layered direction of the three dimensional electrode.

TECHNICAL FIELD

This disclosure relates to an electrode having a three dimensionalstructure with electron directing members extending from the currentcollector and a method of making the three dimensional structure.

BACKGROUND

Hybrid vehicles (HEV) and electric vehicles (EV) usechargeable-dischargeable power sources. Secondary batteries such aslithium-ion batteries are typical power sources for HEV and EV vehicles.Lithium-ion secondary batteries typically use carbon, such as graphite,as the anode electrode. Graphite materials are very stable and exhibitgood cycle-life and durability. However, graphite material suffers froma low theoretical lithium storage capacity of only about 372 mAh/g. Thislow storage capacity results in poor energy density of the lithiumionbattery and low electric mileage per charge.

To increase the theoretical lithium storage capacity, silicon has beenadded to active materials. However, silicon active materials suffer fromrapid capacity fade, poor cycle life and poor durability. One primarycause of this rapid capacity fade is the massive volume expansion ofsilicon (typically up to 300%) upon lithium insertion. Volume expansionof silicon causes particle cracking and pulverization. Thisdeteriorative phenomenon escalates to the electrode level, leading toelectrode delamination, loss of porosity, electrical isolation of theactive material, increase in electrode thickness, rapid capacity fadeand ultimate cell failure.

SUMMARY

Disclosed herein are methods of making a three dimensional electrodehaving an active material. One method of making the three dimensionalelectrode having the active material layered between a current collectorand a separator includes growing nanotubes at predetermined points on afirst sheet of electron directing material, wherein the electrondirecting material is highly conductive and chemically inert; aligningthe nanotubes in a direction perpendicular to the first sheet;functionalizing a distal end of each nanotube; bonding a second sheet ofelectron directing material to the functionalized distal end of eachnanotube; depositing magnetic particles along the second sheet; applyinga magnetic field to the magnetic particles to rotate the first sheet,the second sheet and the nanotubes ninety degrees to form an electrondirecting structure; and attaching the electron directing structure on asurface of the current collector with a polymer binder. The electrondirecting structure is configured to direct electron flow along alayered direction of the three dimensional electrode.

Another method of making a three dimensional electrode for a battery asdisclosed herein includes growing carbon nanotubes at predeterminedpoints on a first sheet of graphene; decorating the carbon nanotubeswith magnetic particles; aligning the nanotubes in a directionperpendicular to the first sheet by applying a magnetic force to themagnetic particles; functionalizing a distal end of each nanotube;bonding a second sheet of graphene to the functionalized distal end ofeach nanotube; depositing additional magnetic particles along the secondsheet; applying a magnetic field to the additional magnetic particles torotate the first sheet, the second sheet and the nanotubes ninetydegrees to form an electron directing structure; and attaching theelectron directing structure on a surface of a current collector with apolymer binder.

These and other aspects of the present disclosure are disclosed in thefollowing detailed description of the embodiments, the appended claimsand the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.Included in the drawings are the following figures:

FIG. 1 is a perspective view of a three dimensional electrode asdisclosed herein showing a current collector and an embodiment ofelectron directing members;

FIG. 2 is a perspective view of another three dimensional electrode asdisclosed herein showing a current collector and another embodiment ofelectron directing members;

FIG. 3 is a cross section view of FIG. 1 along line 3-3;

FIG. 4 is a cross sectional view of FIG. 1 along line 3-3 and includingactive material;

FIGS. 5A-5D are schematics of a method of making a three dimensionalelectrode as disclosed herein; and

FIG. 6 is a flow diagram of a method of making the three dimensionalelectrode schematically illustrated in FIGS. 5A-5D.

DETAILED DESCRIPTION

Because the carbon material used in electrodes of conventionalbatteries, such as lithium ion batteries or sodium ion batteries,suffers from a low specific capacity, the conventional battery has poorenergy density even though there is small polarization and goodstability. Furthermore, batteries having electrodes of graphite or othercarbon materials develop increased internal resistance over time, whichdecreases their ability to deliver current.

To address the poor energy density of carbon based electrodes,alternative active materials with higher energy densities are desired.Silicon, tin, germanium and their oxides and alloys are non-limitingexamples of materials that may be added to an electrode active materiallayer to improve its energy density, among other benefits. Oneparticular example is the use of silicon in lithium-ion batteries.Silicon based anode active materials have potential as a replacement forthe carbon material of conventional lithium-ion battery anodes due tosilicon's high theoretical lithium storage capacity of 3500 to 4400mAh/g. Such a high theoretical storage capacity could significantlyenhance the energy density of the lithium-ion batteries. However,silicon active materials suffer from rapid capacity fade, poor cyclelife and poor durability. One primary cause of this rapid capacity fadeis the massive volume expansion of silicon (typically up to 300%) uponlithium insertion. Volume expansion of silicon can cause particlecracking and pulverization when the silicon has no room to expand. Thisexpansion can lead to electrode delamination, electrical isolation ofthe active material, capacity fade due to collapsed conductive pathways,and, like carbon based electrodes, increased internal resistance overtime, which decreases their ability to deliver current.

Disclosed herein are three dimensional electrode structures designed tocounter this increased internal resistance caused by breakdown orexpansion of the active material of battery electrodes. The threedimensional electrode structures have electron directing members thatmaintain substantially vertical conductive pathways throughout the lifeof the battery and increase lithium ion storage due to use of increasedgraphite in the electrode. As used herein, “vertical” refers to thestacking, or layered, direction of the electrode.

A three dimensional electrode has an active material layered between acurrent collector and a separator. FIG. 1 is an example of a threedimensional electrode 10 with the active layer and separator removed tobetter describe the structure. The three dimensional electrode 10 inFIG. 1 has a current collector 12 and electron directing members 14extending from a surface 16 of the current collector 12. The electrondirecting members 14 are configured to direct electron flow e along alayered direction A of the three dimensional electrode 10.

The material of the current collector 12 can be a metal foil such asnickel, iron, copper, aluminum, stainless steel and carbon, asnon-limiting examples, as well as any other material known to thoseskilled in the art for the electrode applications. The current collector12 can have a thickness in the range of about 5 μm to about 15 μm.

The electron directing members 14 are sheets 18 of highly conductive andchemically inert material aligned vertically along the surface 16 of thecurrent collector 12, as illustrated in FIGS. 1-4. The sheets 18 can be,as a non-limiting example, graphene sheets.

The electron directing members 14 can be a plurality of sheets 18 eachhaving the same length and height, as illustrated in FIG. 1. The lengthof the plurality of sheets 18 can span the length or width of thecurrent collector 12, depending on the alignment of the sheets on thecurrent collector 12. The plurality of sheets 18 can include sheets 18of different lengths, as illustrated in FIG. 2, with the sheets 18′spanning only a partial length or partial width of the current collector12. A perimeter edge 19 of each sheet 18 is attached to the surface 16of the current collector 12 with a polymer binder.

As illustrated in FIGS. 1 and 2, each pair of adjacent verticallyaligned sheets 18 is separated by one or more horizontal nanotubes 20grown from a sputtered metal 22 on one of the pair of adjacentvertically aligned sheets 18 and attached to the other of the pair ofadjacent vertically aligned sheets 18 with a functional group 24. Asused herein, “horizontal” refers to a direction substantiallyperpendicular to the current collector. As illustrated in FIGS. 1 and 2,three nanotubes 20 and two nanotubes 20 are shown, respectively, betweeneach pair of sheets 18 by means of example only. The number of nanotubes20 between a pair of adjacent sheets 18 is configured to support thepair of sheets 18 during alignment on the current collector 12. As anon-limiting example, the nanotubes 20 can be spaced such that each ofthe plurality of nanotubes 20 is separated from another nanotube 20 bybetween 20-50 nanometers.

The nanotubes 20 can be carbon nanotubes or can be of a magneticmaterial. The nanotubes 20 can be other tubular structured metal such aszinc oxide, titanium dioxide and others. The functional group 24 can beany functional group that will bond a particular nanotube 20 to thematerial of the sheet 18. As a non-limiting example, carboxylic acid canbe used as the functional group 24 when the sheet 18 is graphene.

FIG. 3 is a cross sectional view of the three dimensional electrode ofFIG. 1 along line 33, illustrating how the electron directing members 14comprise sheets that are substantially vertical to the surface 16 of thecurrent collector 12, with the nanotubes 20 substantially horizontal tothe surface 16 of the current collector 12.

FIG. 4 is the cross sectional view of FIG. 3 with the electrode 40including the active material layer 26 formed on the current collector12 with the separator 28 above the active material layer 26. The sheets18 are surrounded by the active material layer 26 and extend into theactive material layer 26 to direct electrons in a substantially verticalpath through the active material layer 26, reducing the amount ofelectrons taking a longer path through the active material layer 26. Forexample, electron flow substantially horizontal to the current collector12 is reduced. Over the life of the electrode, the electron directingmembers 14 maintain conductive pathways, slowing the increase ofinternal resistance and accordingly increasing battery life. When thesheets 28 are graphene, lithium ion storage is also improved.Furthermore, the electron directing members 14 assist in restrainingexpansion of active material such as silicon to two dimensions, reducingissues that occur from large volume expansion, such as particle crackingand pulverization, electrode delamination, electrical isolation of theactive material, capacity fade due to collapsed conductive pathways, andincreased internal resistance over time, which decreases their abilityto deliver current.

As illustrated in FIG. 4, each sheet 18 has a free end 30 spaced fromthe separator 28. The sheets 18 can extend through the entire activematerial layer 26, as illustrated, or can have a length less than thethickness of the active material layer 26. As a non-limiting example,the sheets 18 can have a height of between about 50 and 60 microns, solong as the distal ends 30 do not contact the separator 28. Thethickness of the electrode 40 is typically about 60 nanometers. Thesheets 18 can all have the same height or can have varying heights.

Also disclosed herein are batteries made with the three dimensionalelectrodes 10,10′, 40 disclosed herein. For example, lithium ionbatteries can be include the three dimensional electrodes disclosedherein. The three dimensional electrodes can be utilized as anodes,incorporating active material including, as non-limiting examples,silicon, tin and germanium, with graphite or other carbon basedmaterial. The silicon material can be silicon, a silicon alloy, asilicon/germanium composite, silicon oxide and combinations thereof. Thetin material can be tin, tin oxide, a tin alloy and combinationsthereof. Other high energy density materials known to those skilled inthe art are also contemplated. The carbon material can include one ormore of graphene, graphite, surface modified graphite, carbon nanotubes,carbon black, hard carbon, soft carbon and any other carbon materialsknown to those skilled in the art having the requisite electrochemicaldimensional electrodes 10, 10′, 40 are also disclosed herein. FIGS.5A-5D are schematics of the three dimensional electrode 10 being formed.FIG. 6 is a flow diagram of the methods disclosed herein.

In FIG. 5A and step S100 of FIG. 6, a metal 22 is sputtered on theelectron directing material, a sheet 18 of highly conductive andchemically inert material. Nanotubes 20 are gown in step S102 atpredetermined points on the first sheet 18 of electron directingmaterial. Chemical vapor deposition or other means known to thoseskilled in the art to grow nanotubes can be used. As shown, thenanotubes 20 can grow in any direction. The nanotubes 20 are aligned toa substantially vertical position, or substantially perpendicular to thesheet 18, by depositing one or more magnetic particles along thenanotubes 20 in step S104 and then applying a magnetic field in stepS106 to the nanotubes 20 to pull the nanotubes 20 into the verticalposition. As a non-limiting example, iron magnetic particles can bedeposited onto the nanotubes 20. Alternatively, if the nanotubes 20 aremade of a magnetic material, step S 104, depositing the nanotubes 20with the magnetic material, can be eliminated as the magnetic field willwork directly on the nanotubes 20 to vertically align the nanotubes 20.

In FIG. 5B and step S 108, the aligned nanotubes 20 are functionalizedat a distal end 32 of each nanotube 20. The nanotubes 20 arefunctionalized with a functional group 24 capable of bonding withanother sheet 18′ of the electron directing material. As a non-limitingexample, if the second sheet 18′ is graphene, the functional group 24can be carboxylic acid. When functionalized, the second sheet 18′ isbonded to the functional group 24 on the nanotubes 20 to form a pair ofadjacent sheets 18, 18′ in step S110.

As shown in FIG. 6, the nanotubes 20 can be functionalized in step S104′prior to depositing the magnetic material onto the nanotubes 20 in stepS106′. The magnetic field is then applied in step S108′ to align thenanotubes 20, and once aligned, the second sheet 18′ is bonded to thefunctional group 24 of the nanotubes 20 in step S110.

As shown in FIG. 5C and FIG. 6, additional magnetic particles 22 aredeposited along the second sheet 18′ in step S112. As a non-limitingexample, iron magnetic particles can be deposited onto the second sheet18′. The magnetic field is applied to the magnetized pair of sheets 18,18′ in step S114 to rotate the pair of sheets 18, 18′ ninety degrees toform an electron directing structure 14.

In FIG. 5D and step 5116 of FIG. 6, the electron directing structure 14is attached to the surface 16 of the current collector 12 with a polymerbinder. The current collector 12 and electron directing structure 14 canbe hot-pressed is required, or can be hot-pressed after the activematerial layer 26 is added and dried.

All combinations of the embodiments are specifically embraced by thepresent invention and are disclosed herein just as if each and everycombination was individually and explicitly disclosed, to the extentthat such combinations embrace operable processes and/ordevices/systems. In addition, all sub-combinations listed in theembodiments describing such variables are also specifically embraced bythe present device and methods and are disclosed herein just as if eachand every such sub-combination was individually and explicitly disclosedherein.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

What is claimed is:
 1. A method of making a three dimensional electrodehaving an active material layered between a current collector and aseparator, the method comprising: growing nanotubes at predeterminedpoints on a first sheet of electron directing material, wherein theelectron directing material is highly conductive and chemically inert;aligning the nanotubes in a direction perpendicular to the first sheet;functionalizing a distal end of each nanotube; bonding a second sheet ofelectron directing material to the functionalized distal end of eachnanotube; depositing magnetic particles along the second sheet; applyinga magnetic field to the magnetic particles to rotate the first sheet,the second sheet and the nanotubes ninety degrees to form an electrondirecting structure; and attaching the electron directing structure on asurface of the current collector with a polymer binder, wherein theelectron directing structure is configured to direct electron flow alonga layered direction of the three dimensional electrode.
 2. The method ofclaim 1, wherein growing the nanotubes comprises: sputtering a metal ona surface of the first sheet; and growing the nanotubes with chemicalvapor deposition.
 3. The method of claim 2, wherein the metal ismagnetic, growing magnetic nanotubes, and aligning the nanotubescomprises applying a magnetic field to the nanotubes.
 4. The method ofclaim 1 further comprising: depositing the active material layer on thecurrent collector such that the electron directing structure extendsalong a thickness of the active material layer.
 5. The method of claim 4further comprising: layering electrolyte and the separator on the activematerial layer, wherein the end of the electron directing structureopposite the current collector is in spaced relation to the separator.6. The method of claim 1, further comprising: hot-pressing the electrondirecting structure and the current collector.
 7. The method of claim 1,wherein the nanotubes are a non-magnetic material and aligning thenanotubes comprises: depositing a magnetic particle on each nanotube;and applying a magnetic field to the magnetic particle.
 8. The method ofclaim 1, wherein the nanotubes are carbon nanotubes.
 9. The method ofclaim 1, wherein the electron directing material is graphene.
 10. Themethod of claim 1, wherein the nanotubes are functionalized withcarboxylic acid.
 11. The method of claim 1, wherein the nanotubes arespaced from each other by a range of 20-50 nanometers.
 12. The method ofclaim 1, wherein the electron directing structure has a height ofbetween about 50 and 60 microns.
 13. The method of claim 1, furthercomprising: after bonding the second sheet, growing nanotubes atpredetermined points on the second sheet; aligning the nanotubes in adirection perpendicular to the second sheet; functionalizing a distalend of each nanotube; bonding a third sheet of electron directingmaterial to the functionalized distal end of each nanotube; anddepositing magnetic particles along a surface of the third sheet priorto applying the magnetic field to the magnetic particles.
 14. A methodof making a three dimensional electrode for a battery, the methodcomprising: growing carbon nanotubes at predetermined points on a firstsheet of graphene; decorating the carbon nanotubes with magneticparticles; aligning the nanotubes in a direction perpendicular to thefirst sheet by applying a magnetic force to the magnetic particles;functionalizing a distal end of each nanotube; bonding a second sheet ofgraphene to the functionalized distal end of each nanotube; depositingadditional magnetic particles along the second sheet; applying amagnetic field to the additional magnetic particles to rotate the firstsheet, the second sheet and the nanotubes ninety degrees to form anelectron directing structure; and attaching the electron directingstructure on a surface of a current collector with a polymer binder. 15.The method of claim 14 further comprising: layering an active materiallayer on the current collector and around the electron directingstructure, wherein the electron directing structure is configured todirect electron flow along a layered direction of the three dimensionalelectrode.
 16. The method of claim 15 further comprising: layeringelectrolyte and the separator on the active material layer, wherein theend of the electron directing structure opposite the current collectoris in spaced relation to the separator.
 17. The method of claim 14,wherein the nanotubes are functionalized with carboxylic acid.
 18. Themethod of claim 14, wherein the nanotubes are spaced from each other bya range of 20-50 nanometers.
 19. The method of claim 14, wherein theelectron directing structure has a height of between about 50 and 60microns.